The present invention relates to a memory device, and more particularly to a dynamic type semiconductor memory device fabricated on a semiconductor chip.
Dynamic type memory device employing single transistor (one transistor) type memory cells are widely used. In this type of memory device, a plurality of memory cells are disposed at intersections of address lines and digit lines, as is well known, and a plurality of sense amplifiers are provided for respective digit line pairs. As the sense amplifiers, the structures disclosed by U.S. Pat. Nos. 3,588,844 and 3,514,765 issued to Christensen have been known. In this system, the digit line is devided into equal parts and connected to a balanced or differential amplifier. This type of system has been widely employed with varying degrees of success. However, various embodiments of this type system of necessarily consume D.C. power.
In this connection, a memory system employing a dynamic type sense amplifier having no load elements was proposed by U.S. Pat. No. 4,061,954 issued to Proebsting et.al. In this system, true and complement digit lines are connected through resistances to input nodes of an amplifier comprised of cross-coupled transistors. This system consumes no D.C. power.
However, in this system, the sense amplifier has no capability to drive the digit line toward a high potential. Therefore, if a single input/output (I/O) bus line structure is employed for saving wiring space in which only one digit line of the digit line pair is connected to the I/O bus line and the other digit line is left alone, it is difficult to drive the mentioned other digit line to the high potential on a write operation in comparison to the case that the mentioned one digit line is driven to the high level through the I/O bus line. This results in failure of the write operation. Therefore, it has been difficult to incorporate the mentioned dynamic type sense amplifier into the single bus line structure of the memory.
Hence, a memory device of a high-density and operable with high-stability has been desired.